1. Field of the Invention
The present invention relates to an information signal processing technique and, more specifically, to a data sampling method and device for converting an analog input signal to a digital output signal by using an A/D (analog-to-digital) sampling frequency.
2. Description of the Prior Art
In recent years, the technology relating to mobile communication terminals has made great progress. As a result, mobile communication terminals having various communication functions such as a function of communicating various data including audio data, facsimile data, and personal computer (PC) data have been developed. To implement such communication functions, it is indispensable to incorporate, in a mobile communication terminal, an A/D conversion function for converting an analog signal to a digital signal. The A/D conversion is realized in such a manner that a digital signal is generated by sampling an analog signal according to an A/D sampling frequency. Techniques relating to this type of sampling are disclosed in Japanese Patent Application Laid-Open Nos. 6-313764, 9-83588, 9-135149, 9-321632, 8-4591, etc.
One problem that arises in incorporating various communication functions as described above in mobile communication terminals is that various data to be handled have different frequencies. As is well known, in mobile communication terminals, output signals should have the same frequency even if input signals have different frequencies. However, in the A/D conversion method in which a digital signal is generated by merely sampling an analog signal according to a sampling frequency, output signals have different frequencies when input signals have different frequencies. Although various A/D conversion techniques have been proposed to solve this problem, all of them are complex in configuration and hence are difficult to implement.